I recently added 10 lbs of nice looking liverock to my newly started clown fish tank. When the rock went in it was a beautiful white color that looked amazing under my light. Now it is starting to turn green (algae?) how can I keep it white or what is the appropriate color for rock?

Over time it will chagne color because of the bacteria growth. More time and it should develop coralline growth, and turn either Pink, Red, Purple or Flouresent Green. Die off of some rock will appear black.

Simply getting some adds it to the tank. A friend can give you some scrapings of it to put in the tank. I wouldn't get too excited about the stuff. It is a sign of a tank in good shape, but it still uses up calcium and such that should be going towards your corals and no matter what, any algae can become a nuisance! Getting this hard stuff off of power heads is a chore.